Paper is static, but it is also light, flexible, and robust and has high resolution for reading documents in various scenarios. Digital devices will likely never match paper's flexibility, but they come with all the benefits of computation and networking. Tags provide a simple means of bridging the gap between the two media to get the most out of both. This article explores the trade-offs between two different types of tagging technologies—marker-based and content-based—through the lens of four systems. It extrapolates issues for designers to consider when developing systems that transition between paper and digital content.